Frequency conversion circuit with UHF/VHF common PLL buffer

ABSTRACT

An integrated oscillation circuit used for frequency conversion circuit in which UHF frequency conversion and VHF frequency conversion are selectively energized to use a common IF amplifier. The integrated oscillation circuit is used for a local oscillation circuit. The integrated oscillation circuit including a connection terminal connected to an external resonance circuit and an input line of a mode switching signal which is set at a different level in response to an operation mode, an oscillation element, a bias terminal of which is connected to the connection terminal, a detection circuit detecting the level of the mode switching signal applied to the bias terminal of the oscillation element, and a switching circuit turning on and off a power source for driving the oscillation element in response to the level detected at the detection circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oscillator and a mixer applied to a television tuner performing wide band reception etc.

2. Description of the Related Art

First, an explanation will be made of a related art referring to the drawings.

FIG. 1 is a system block diagram of a usual television tuner circuit for UHF/VHF.

In FIG. 1, ANT denotes a UHF/VHF antenna; STC_(U) a UHF single-tuned circuit; STC_(VH) a VHF "High" single-tuned circuit; STC_(VL) a VHF "Low" single-tuned circuit; AMP_(U) a UHF RF amplifier; AMP_(V) a VHF RF amplifier; DTC_(U) a UHF double-tuned circuit; DTC_(VH) and DTC_(LH) VHF double-tuned circuits; and IC an integrated frequency conversion circuit.

In a VHF operation mode, where the VHF broadcast is received, the television signal received via the antenna ATN is input to single-tuned circuits STC_(VH) and STC_(VL). In the single-tuned circuits STC_(VH) and STC_(VL), the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP_(V). The RF amplifier AMP_(V) is constituted by for example a dual gate MOS FET (metal oxide semiconductor field effect transistor), the outputs of the single-tuned circuits STC_(VH) and STC_(VL) are output to one gate, an AGC voltage is input to the other gate, and the high frequency output is extracted. The high frequency output of the RF amplifier AMP_(V) is subjected to a predetermined tuning function by the double-tuned circuits DTC_(VH) and DTC_(VL), and then input to the mixing circuit MIX_(V) of the integrated frequency conversion circuit IC. In the mixing circuit MIX_(V), mixing with the local oscillation frequency signal S_(LV) by the local oscillation circuit OSC_(V) having a frequency higher than the frequency of a video image carrier wave signal RF_(V) of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF_(V) which is the frequency of a difference thereof is extracted. This is output to the IF amplifier AMP_(IF) commonly used for UHF and VHF. In the IF amplifier AMP_(IF), the predetermined amplification function is carried out, so that the IF output of VHF is obtained.

In a UHF operation mode, when a UHF broadcast is received, the television signal of the UHF band received via the antenna ATN is input to the single-tuned circuit STC_(U). In the single-tuned circuit STC_(U), the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP_(U). The RF amplifier AMP_(U) is constituted by for example the dual gate MOS FET. TO one gate is input the output of the single-tuned circuit STC_(U), and to the other gate is input the AGC voltage, so that the high frequency output is extracted. The high level frequency output of the RF amplifier AMP_(V) is subjected to the predetermined tuning function by the double-tuned circuit DTC_(U), then input to the mixing circuit MIX_(U) of the integrated frequency conversion circuit IC. In the mixing circuit MIX_(U), mixing with the local oscillation frequency signal S_(LU) by the local oscillation circuit OSC_(U) having a frequency higher than the video image carrier wave frequency of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF_(U) which is the frequency of the difference thereof is extracted. This is output to the IF amplifier AMP_(IF), commonly used for UHF and VHF. In the IF amplifier AMP_(IF), the predetermined amplification function is carried out, so that the IF output of UHF is obtained.

The integrated frequency conversion circuit IC is constituted by a VHF circuit of a VHF local oscillation circuit OSC_(V) and a mixing circuit MIX_(V) thereof, a UHF circuit of a UHF local oscillation circuit OSC_(U) and a mixing circuit MIX_(U) thereof, and an IF amplifier AMP_(IF) which amplifies an intermediate frequency signal IF_(V) from the VHF mixing circuit MIX_(V) and an intermediate frequency signal IF_(U) from the UHF mixing circuit MIX_(U).

In the integrated frequency conversion circuit IC in the above-mentioned tuning circuit, to achieve a reduction of consumption of electric power and simplify a circuit construction, the IF amplifier AMP_(IF) is used in common, and therefore the VHF circuit of the VHF local oscillation circuit OSC_(V) and the mixing circuit MIX_(V), and the UHF circuit of the UHF local oscillation circuit OSC_(U) and the mixing circuit MIX_(U) are selectively operated in accordance with either the VHF or UHF mode. More specifically, a UHF/VHF mode changing signal (not shown) is input to the integrated frequency conversion circuit IC from an outside control system to drive a switching circuit (not shown), whereby current sources for driving the respective circuit in the UHF circuit or the respective circuit in the VHF circuit are turned ON or OFF.

An explanation will be made below of a concrete circuit structure of a general VHF local oscillation circuit OSC_(V), UHF local oscillation circuit OSC_(U), switching circuit, a VHF mixing circuit MIX_(V), and a UHF mixing circuit MIX_(U) in the integrated frequency conversion circuit IC with reference to FIG. 2 to FIG. 4.

FIG. 2 is a circuit diagram showing an example of the circuit configuration of a VHF local oscillation circuit OSC_(V) and an output buffer thereof. OSC_(V) denotes a VHF local oscillation circuit; RSN an external variable resonance circuit; and BUF_(V) an output buffer, respectively.

The VHF local oscillation circuit OSC_(V) and the output buffer BUF_(V) are integrated. The VHF local oscillation circuit OSC_(V) is connected via three input/output terminals T₁ to T₃, which are connection terminals for an external circuit etc., to the external variable resonance circuit RSN_(V).

The VHF local oscillation circuit OSC_(V) is constituted as a positive feedback differential amplifier type oscillation circuit, consisting of npn-type transistors Q₁ and Q₂ functioning as an oscillator, a constant voltage source V₁ for biasing the npn-type transistors Q₁ and Q₂, resistance elements R₁, R₂, and R₃, and a constant current source I₁.

The base of the oscillation transistor Q₁ is connected to the input/output terminal T₁, connected via the resistance element R₁ to the constant voltage source V₁, and further connected to the base of the npn-type transistor Q₄ of the output buffer BUF_(V). The emitter of the oscillation transistor Q₁ is connected to the constant current source I₁, and another terminal of the constant current source I₁ is grounded. The collector of the oscillation transistor Q₁ is connected to a line feeding a power source voltage V_(CC).

The base of the oscillation transistor Q₂ is connected to the input/output terminal T₃, connected via the resistance element R₂ to the constant voltage source V₁ and further connected to the base of the npn-type transistor Q₃ of the output buffer BUF_(V). The emitter of the oscillation transistor Q₂ is connected to the constant current source I₁ and the collector thereof is connected to the input/output terminal T₂. Also, the resistance element R₃ is connected between the line of the power source voltage V_(CC) and the collector of the oscillation transistor Q₂.

The external variable resonance circuit RSN₁ is constituted by a variable capacitance capacitor CV₁ and a coil L₂ which are connected in parallel. A connection point of one end of the coil L₂ of the external variable resonance circuit RSN₁ and one electrode of the variable capacitance capacitor CV₁ is grounded. A connection point of the other end of the coil L₂ and the other electrode of the variable capacitance capacitor CV₁ is connected via the capacitor C₁ and the input/output terminal T₁ to the base of the oscillation transistor Q₁, and connected via the capacitor C₂ and the input/output terminal T₂ to the collector of the oscillation transistor Q₂. Also, one electrode of a capacitor C₃ is connected to an input/output terminal T₃, and the other electrode of the capacitor C₃ is grounded.

The VHF local oscillation circuit OSC_(V) is subjected to a positive feedback of the externally attached capacitor C₁ connected via the input/output terminals T₁ and T₂ to the base of the oscillation transistor Q₁. It oscillates at the resonance frequency of the external variable resonance circuit RSN₁ and outputs the resonance signal to the output buffer BUF_(V).

The output buffer BUF_(V) is constituted by npn-type transistors Q₃ and Q₄, resistance elements R₅ to R₇ functioning as load resistor, resistance elements R₈ to R₁₁, and the constant current source I₂.

The base of the transistor Q₃ is connected to the base of the oscillation transistor Q₂ of the local oscillation circuit OSC_(V) as mentioned above, the emitter is connected via the resistance elements R₈ and R₉, connected in series, to the constant current source I₂, and another terminal of the constant current source I₂ is grounded. The collector of the transistor Q₃ is connected via the series-connected load resistance elements R₆ and R₅ to the line of the power source voltage V_(CC).

Note that, the output terminal O_(UT1V) of the local oscillation circuit for VHF is constituted by the connection point of the resistance element R₈ and the resistance element R₉. This output terminal O_(UT1V) is connected to the integrated VHF mixing circuit MIX_(V) in FIG. 1.

The base of the transistor Q₄ is connected to the base of the oscillation transistor Q₁ of the local oscillation circuit OSC_(V) as mentioned above, and the emitter is connected via series-connected resistance elements R₁₀ and R₁₁ to the constant current source I₂. The collector of the transistor Q₄ is connected via the load resistance element R₇ to the connection point of the series-connected load resistance elements R₇ and R₅.

Note that the output terminal O_(UT2V) of the VHF local oscillation circuit OSC_(V) is constituted by the connection point of the resistance element R₁₀ and the resistance element R₁₁. This output terminal O_(UT2V) is connected to the integrated VHF mixing circuit MIX_(V) in FIG. 1.

FIG. 3 is a circuit diagram showing one example of the configuration of the UHF local oscillation circuit OSC_(U) and switching circuit. In FIG. 3, OSC_(U) denotes a UHF local oscillation circuit; SW denotes a switching circuit; and an RSN₂ denotes an external variable resonance circuit, respectively.

The UHF local oscillation circuit OSC_(U) and the switching circuit SW are integrated. The UHF local oscillation circuit OSC_(U) is connected via four input/output terminals T₅ to T₈, which are connection terminals to an external circuit etc., to the external variable resonance circuit RSN₂.

Also, a UHF/VHF mode changing signal S_(SW) is applied to the switching circuit SW via the switching terminal T₄ provided separately from the input/output terminals T₅ to T₈.

The UHF local oscillation circuit OSC_(U) is constituted by a differential operation type Colpitz oscillation circuit, consisting of npn-type transistors Q₇ and Q₈ used for oscillation, a constant voltage source V₂ biasing the oscillation non-type transistors Q₇ and Q₈, resistance elements R₁₃ and R₁₄, resistance elements R₁₅ and R₁₆ functioning as load resistors of the oscillation npn-type transistors Q₇ and Q₈, and constant current sources I₃ and I₄.

The base of the oscillation transistor Q₇ is connected to the input/output terminal T₅ and, connected via the resistance element R₁₃ to the constant voltage source V₂. The emitter of the oscillation transistor Q₁ is connected to the input/output terminal T₆ and connected to the constant current source I₃, and the other terminal of the constant current source I₃ is grounded. The collector of the oscillation transistor Q₇ is connected via the load resistance element R₁₅ to the line of the power source voltage V_(CC), and the output terminal O_(UT1U) of the differential operation type Colpitz oscillation circuit is constituted by the connection point of the collector of the oscillation transistor Q₇ and the load resistance element R₁₅. This output terminal O_(UT1U) is connected to the integrated mixing circuit MIX_(U) in FIG. 1.

The base of the oscillation transistor Q₈, is connected to the input/output terminal T₈, and connected via the resistance element R₁₄ to the constant voltage source V₂. The emitter of the oscillation transistor Q₈ is connected to the input/output terminal T₇ and connected to the constant current source I₄, and the other terminal of the constant current source I₄ is grounded. The collector of the oscillation transistor Q₈, is connected via the load resistance element R₁₆ to the line of the power source voltage V_(CC), and the output terminal O_(UT2U) of the differential operation type Colpitz oscillation circuit is constituted by the connection point of the collector of the oscillation transistor Q₈, and the load resistance element R₁₆. This output terminal O_(UT2U) is connected to the integrated mixing circuit MIX_(U).

The external variable resonance circuit RSN₂ is constituted by connecting a capacitor C₅ in parallel to the serial circuit of a variable capacitance capacitor CV₂ and a coil L₃. The connection point of the coil L₃ of the external variable resonance circuit RSN₂ and the capacitor C₅ is connected via a DC cutting capacitor C₆ and the input/output terminal T₅ to the base of the oscillation transistor Q₇, and the connection point of an anode of the variable capacitance diode CV₂ and the capacitor C₅ is connected via the DC cutting capacitor C₇ and the input/output terminal T₈ to the base of the oscillation transistor Q₈.

Also, a positive feedback capacitor C₈ is connected between the connection point of the capacitor C₆ and input/output terminal T₅ and the input/output terminal T₆, and a positive feedback capacitor C₉, is connected between the connection point of the capacitor C₇ and input/output terminal T₈, and the input/output terminal T₇.

Further, a coupling capacitor C₁₀ is connected to the connection point of the capacitor C₈ and the input/output terminal T₆ and the connection point of the capacitor C₉ and the input/output terminal T₇, i.e., between the emitter of the oscillation transistor C₅ and the emitter of the oscillation transistor Q₈. The UHF local oscillation circuit OSC_(U) is subjected to a positive feedback of the externally attached capacitors C₈ and C₉ connected to the base and emitter of the oscillation transistors Q₇ and Q₈ via the input/output terminals T₅, T₆, T₇, and T₈. It oscillates by the resonance frequency of the external variable resonance circuit RSN₂ connected to the respective bases of the oscillation transistors Q₇ and Q₈ and outputs a local oscillation frequency signal S_(LU) having a predetermined frequency from the output terminals O_(UT1U) and O_(UT2U) to the UHF mixing circuit MIX_(U).

Note that, the oscillation transistors Q₇ and Q₈ constituting the differential operation type Colpitz oscillation circuit are mutually connected at their respective bases via the external variable resonance circuit RSN₂ and therefore perform oscillation operations of out of phases. Accordingly, local oscillation frequency signals S_(LU) having out of phases to each other are output from the output terminals O_(UT1T) and O_(UT2U).

The switching circuit SW is constituted by the switching operation npn-type transistors Q₅ and Q₆ and resistance elements R₁₈, R₁₉, and R₂₀.

The base of the switching transistor Q₅ is connected via the resistance element R₁₈ to the collector of the switching transistor Q₆, the emitter thereof is grounded, and the collector is connected to the not illustrated UHF system current source. The base of the switching transistor Q₆ is connected via the resistor R₂₀ to the switching terminal T₄, the emitter thereof is grounded, the connection point of the collector and the resistance element R₁₈ is connected via a high resistance element R₁₉ to the line of the power source voltage V_(CC), and the connection point of the collector and the resistance element R₁₈ and the connection point with the high resistance element R₁₉ is connected to the not illustrated VHF system current source.

FIG. 4 is a circuit diagram showing an example of the circuit configuration of the VHF mixing circuit MIX_(V) and the UHF mixing circuit MIX_(U). These circuits are integrated.

The VHF mixing circuit MIX_(V) is constituted by npn-type transistors Q₁₁ to Q₁₆, resistance elements R₂₁ to R₂₃, and constant current sources I₆ and I₇.

The base of the transistor Q₁₁ is connected to the output of the VHF local oscillation circuit OSC_(V) and the base of the transistor Q₁₄. The emitter of the transistor Q₁₁ is connected to the emitter of the transistor Q₁₂ and the collector of the transistor Q₁₅. The collector of the transistor Q₁₁ is connected via the resistance element R₂₁ to the line of the power source voltage V_(CC), and the connection point of the collector and the resistance element R₂₁ is connected to one input of the IF amplifier AMP_(IF).

The base of the transistor Q12_(V) is connected to the output of the VHF local oscillation circuit OSC_(V) and the base of the transistor Q₁₃, and the collector is connected to the other input of the IF amplifier AMP_(IF).

The emitter of the transistor Q₁₃ is connected to the emitter of the transistor Q₁₄ and the collector of the transistor Q₁₆. The collector of the transistor Q₁₃ is connected to the one input of the IF amplifier AMP_(IF).

The collector of the transistor Q₁₄ is connected via the resistance element R₂₂ to the line of the power source voltage V_(CC), while the connection point of the collector and the resistance element R₂₂ is connected to the other input of the IF amplifier AMP_(IF).

The base of the transistor Q₁₅ is connected to the output of the double-tuned circuits DTC_(VH) and DTC_(VL) shown in FIG. 1, the emitter is connected to the constant current source I₆, and the constant current source I₆ is grounded.

The base of the transistor Q₁₆ is connected to the output of the double-tuned circuits DTC_(VH) and DTC_(VL) shown in FIG. 1, the emitter is connected to the constant current source I₇, and the constant current source I₇ is grounded.

Also, a resistance element R₂₃ is connected between the emitter of the transistor Q₁₅ and the emitter of the transistor Q₁₆. This VHF mixing circuit MIX_(V) mixes the local oscillation frequency signal S_(LV) by the local oscillation circuit OSC_(V) having a frequency higher than the frequency of a video image carrier wave signal RF_(V) of the selected channel by a predetermined frequency, for example, 58.75 MHz, extracts an intermediate frequency signal IF_(V) which is the frequency of a difference thereof, and outputs the same to the IF amplifier AMP_(IF), commonly used for UHF and VHF.

The UHF mixing circuit MIX_(U) is constituted by npn-type transistors Q₁₈ to Q₂₄, resistance elements R₂₄ to R₂₆, and constant current sources I₈ and 1₉.

The base of the transistor Q₁₈ is connected to the output of the UHF local oscillation circuit OSC_(U) and the base of the transistor Q₂₂. The emitter of the transistor Q₁₈ is connected to the emitter of the transistor Q₁₉ and the collector of the transistor Q₂₃. The collector of the transistor Q₁₈ is connected via the resistance element R₂₄ to the line of the power source voltage V_(CC), and the connection point of the collector and the resistance element R₂₄ is connected to one input of the IF amplifier AMP_(IF).

The base of the transistor Q₁₉ is connected to the output of the UHF local oscillation circuit OSC_(U) and the base of the transistor Q₂₁, and the collector is connected to the other input of the IF amplifier AMP_(IF).

The emitter of the transistor Q₂₁ is connected to the emitter of the transistor Q₂₂ and the collector of the transistor Q₂₄. The collector of the transistor Q₂₁ is connected to one input of the IF amplifier AMP_(IF).

The collector of the transistor Q₂₂ is connected via the resistance element R₂₅ to the line of the power source voltage V_(CC), and the connection point of the collector and the resistance element R₂₅ is connected to the other input of the IF amplifier AMP_(IF).

The base of the transistor Q₂₃ is connected to the output of the double-tuned circuit DTC_(U) shown in FIG. 1, the emitter thereof is connected to the constant current source I₈, and the other terminal of the constant current source I₈ is grounded.

The base of the transistor Q₂₄ is connected to the output of the double-tuned circuit DTC_(U) shown in FIG. 1, the emitter thereof is connected to the constant current source I₉, and other terminal of the constant current source I₉ is grounded.

Also, a resistance element R₂₆ is connected between the emitter of the transistor Q₂₃ and the emitter of the transistor Q₂₄. This UHF mixing circuit MIX_(U) mixes the local oscillation frequency signal S_(LU) by the local oscillation circuit OSC_(U) having a frequency higher than the frequency of a video image carrier wave signal RF_(U) of the selected channel by predetermined frequency, for example, 58.75 MHz, extracts an intermediate frequency signal IF_(U) which is the frequency of a difference thereof, and outputs the same to the IF amplifier AMP_(IF) commonly used for UHF and VHF.

In such a structure, at the VHF operation, the UHF/VHF mode changing signal S_(SW) of a low level "0 V" is input to the switching terminal T₄ by for example the external control system. Alternatively, the switching terminal T₄ is opened. By this, the base potential of the switching transistor Q₆ becomes "0 V", and therefore the switching transistor Q₆ is retained to the OFF state. Accordingly, a current generated via the high resistance element R₁₉ is supplied to the current source for VHF. Along with this, a driving current is supplied to the VHF mixing circuit MIX_(V) and local oscillation circuit OSC_(V). Also, a current generated via the high resistance element R₁₉ is applied via the resistance element R₁₈, as the predetermined signal voltage to the base of the switching transistor Q₅. By this, the switching transistor Q₅ becomes the ON state, and the UHF system current source connected to the collector thereof is turned OFF. Accordingly, the driving current is not supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

In such a VHF operation mode, where the VHF broadcast is received, the television signal received via the antenna ATN is input to single-tuned circuits STC_(VH) and STC_(VL). In the single-tuned circuits STC_(VH) and STC_(VL), the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP_(V). The RF amplifier AMP_(V) is constituted by for example a dual gate MOS FET, the outputs of the single-tuned circuits STC_(VH) and STC_(VL) are output to one gate, an AGC voltage is input to the other gate, and the high frequency output is extracted. The high frequency output of the RF amplifier AMP_(V) is subjected to a predetermined tuning function by the double-tuned circuits DTC_(VH) and DTC_(VL), and then input to the mixing circuit MIX_(V) of the integrated frequency conversion circuit IC. In the mixing circuit MIX_(V), mixing with the local oscillation frequency signal S_(LV) by the local oscillation circuit OSC_(V) having a frequency higher than the frequency of a video image carrier wave signal RF_(V) of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF_(V) which is the frequency of a difference thereof is extracted. This is output to the IF amplifier AMP_(IF) commonly used for UHF and VHF. In the IF amplifier AMP_(IF), the predetermined amplification function is carried out, so that the IF output of VHF is obtained.

Contrary to this, in a UHF operation, a UHF/VHF mode changing signal S_(SW) of a high level "9 V" the same level as that of the power source voltage V_(CC) is applied to the switching terminal T_(SW) by for example the external control system. By this, the base potential of the switching transistor Q₆ becomes the high level, and therefore the switching transistor Q₆ is retained in the ON state. Accordingly, a current generated via the high resistance element R₁₉ flows through the switching transistor Q₆, not supplied to the VHF current source, and the collector side is held at "0 V" at the switching transistor Q₆. Along with this, the driving current is not supplied to the VHF mixing circuit MIX_(V) and local oscillation circuit OSC_(V). Also, the collector side of the switching transistor Q₆ is retained at "0 V", and therefore the base terminal of the switching transistor Q₅ becomes "0 V", whereby the switching transistor Q₅ is retained in the OFF state. By this, the UHF system current source connected to the collector of the switching transistor Q₅ becomes ON. Accordingly, the driving current is supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

In such a UHF operation mode, when a UHF broadcast is received, the television signal of the UHF band received via the antenna ATN is input to the single-tuned circuit STC_(U). In the single-tuned circuit STC_(U), the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP_(U). The RF amplifier AMP_(U) is constituted by for example the dual gate MOS FET. To one gate is input the output of the single-tuned circuit STC_(U), and to the other gate is input the AGC voltage, so that the high frequency output is extracted. The high level frequency output of the RF amplifier AMP_(V) is subjected to the predetermined tuning function by the double-tuned circuit DTC_(U), then input to the mixing circuit MIX_(U) of the integrated frequency conversion circuit IC. In the mixing circuit MIX_(U), mixing with the local oscillation frequency signal S_(LU) by the local oscillation circuit OSC_(U) having a frequency higher than the video image carrier wave frequency of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF_(U) which is the frequency of the difference thereof is extracted. This is output to the IF amplifier AMP_(IF) commonly used for UHF and VHF. In the IF amplifier AMP_(IF), the predetermined amplification function is carried out, so that the IF output of UHF is obtained.

As in the above, in the conventional circuit, a single terminal has been used as the UHF/VHF mode changing terminal T_(SW).

A television tuner etc. handles high frequency signals, and therefore the wiring of the wiring pattern exerts a great influence upon the characteristics.

Also, in an integrated frequency conversion circuit IC comprising integrated mixing circuits MIX_(V) and MIX_(U), local oscillation circuits OSC_(V) and OSC_(U), and the IF amplifier AMP_(IF), when the package becomes large and the inner lead portion from the bare chip to the outside becomes long, there arises problems of a parasitic oscillation and a lowering of the gain due to its parasitic inductance and parasitic capacitance.

Accordingly, an integrated circuit IC for a tuner desirably has as small number of terminals as possible and is accommodated in a small package.

In the above-mentioned conventional circuit of FIG. 3, however, the UHF/VHF mode changing terminal T_(SW) is provided independently besides the four terminals T₅ to T₈ for the connection with the external variable resonance circuit RSN of the local oscillation circuit OSC_(U), and therefore an increase of the number of terminals is caused and also the package size becomes large. For this reason, there are problems of the parasitic oscillation and lowering of gain, and consequently a defect that the enlargement of the size of the tuner and an increase of the costs are induced.

For the reduction of the number of terminals, usually it can be considered to use the three terminals used for the VHF local oscillation circuit OSC_(V) and the UHF local oscillation circuit OSC_(U), but the UHF local oscillation circuit has a high operation frequency, and therefore a differential operation type oscillation circuit is preferable for a stable operation.

In a television tuner etc., the UHF local oscillation circuit has a high operation frequency, and therefore for a stable operation, a differential operation type Colpitz oscillation circuit as shown in FIG. 3 has been used as an oscillator which can stably oscillate over a wide band width.

Accordingly, the four terminals T₅ to T₈ for the connection with the external variable resonance circuit RSN₂ cannot be reduced.

Recently, in a television tuner or mobile radio frequency receiver handling a relatively high frequency signal such as an UHF band or submicrowave band, a further higher stability local oscillator has been required.

So as to satisfy this request, generally there is adopted a method of locking the frequency using for example a PLL (phase locked loop) circuit. As the oscillator used for this, in the frequency conversion circuit of for example a television tuner, a so-called two-output type is ideally used, which can perform output to both of the PLL circuit and the mixing circuit. In the above-mentioned conventional oscillator, however, one oscillation signal output is used for input to the mixing circuit, and therefore the application thereof to locking the frequency using the PLL circuit is difficult.

Here, a case where both of the mixing circuit and the PLL circuit are driven by one oscillation signal output is considered. The mixing circuit and the PLL circuit have optimum input levels, respectively, and therefore a circuit for controlling the level becomes necessary for either of the mixing circuit or the PLL circuit, so that there arises a problem that the circuit becomes complex etc.

Also, when taking a television tuner as an example, the RF signal is input to the mixing circuit in addition to the output of the local oscillator, but where this RF signal is input with a great oscillation width, there is a concern that it will pass the mixing circuit and enter into the PLL circuit. In this case, there is a possibility of a malfunction of the PLL circuit due to the RF signal. For this reason, it must be separated so that the signal is not leaked from the mixing circuit to the PLL circuit. This is cumbersome.

Also, as a method of stably extracting a plurality of oscillation signal outputs, there can be considered a configuration in which a so-called emitter follower EF is added to the output of the oscillator OSC, a configuration in which the buffer amplifier BF is added to the output of the oscillator OSC, or a configuration in which the transistors are connected in cascade. Note that, the loads of the oscillation transistors Q₁ and Q₃ can be constituted using diodes D₁ and D₂.

However, the configuration of loading the emitter follower EF and the configuration of adding the buffer amplifier BF involve the problem of an increase of the consumed electric current.

In the configuration of connecting the transistors in cascade, one level's worth of an excess application voltage is necessary, and therefore it is not suitable for the lowering of voltage. Particularly, when the number of the outputs is increased, there is a defect that the application voltage must be increased by that amount.

Further, in a television tuner, ideally use is made of a so-called two-output type in which output to both of the PLL circuit and mixing circuit is possible.

In the local oscillation circuit used in the conventional integrated frequency conversion circuit IC mentioned above, the VHF local oscillation circuit OSC_(V) is constituted so as to obtain the oscillation signal output via the output buffer BUF_(V), and therefore, in addition to the output from the emitter side of the transistors Q₃ and Q₄ of the output buffer BUF_(V) to the mixing circuit MIX_(V), the oscillation signal output is obtained from the points of connection between the collectors of the transistors Q₃ and Q₄ and the load resistance elements R₆ and R₇. These outputs can be made the outputs to the PLL circuit.

However, in the UHF local oscillation circuit OSC_(U), only one oscillation signal output is input to the mixing circuit MIX_(U), and therefore application is difficult to locking the frequency using the PLL circuit.

It is also possible to consider a configuration in which a plurality of oscillation transistors constituting a Colpitz oscillation circuit are connected in parallel to obtain a plurality of outputs, and one among them is used for the PLL circuit, but in this case, the number of the output systems to the PLL circuit becomes two, i.e. a signal output from the output buffer BUF_(V) of the VHF local oscillation circuit OSC_(V) and a signal output from the UHF local oscillation circuit OSC_(U). For inputting an oscillation signal to the PLL circuit basically having one input, it becomes necessary to provide a switching circuit etc., resulting in problems that the connection to the PLL circuit is cumbersome, the number of elements is increased, and so on.

Also, irrespective of the fact that the VHF mixing circuit MIX_(V) and the UHF mixing circuit MIX_(U) output the intermediate frequency signals IF_(V) and IF_(U) obtained as a result of mixing to the common IF amplifier AMP_(IF) and, as shown in FIG. 4, both circuits have a similar structure, they are quite separately constituted, and therefore there are problems in that an increase of number of components is induced, and thus the increase of costs and enlargement of size are caused.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an integrated oscillation circuit which can achieve a reduction of the number of terminals in a high frequency IC etc., can achieve a reduction of the parasitic oscillation and lowering of gain, and can achieve a reduction of size of the applied tuner etc. and a reduction of cost.

Another object of the present invention is to provide an integrated oscillation circuit in which a balanced output of a plurality of oscillation signals is obtained by a simple circuit without influence exerted upon the oscillation characteristics and in which a reduction of consumption of electric power can be achieved.

Still another object of the present invention is to reduce the number of terminals of the IC by providing a circuit which extracts an oscillation output signal from a plurality of oscillators to a plurality of mixers.

According to the present invention, there is provided an oscillator including, a first oscillating circuit including a first transistor connected to a first resonance circuit and a first load element, the first transistor outputting a first oscillation signal having a first frequency; and a second oscillating circuit including a second transistor connected to a second resonance circuit and a second load element, the second transistor outputting a second oscillation signal having a second frequency. The first transistor and the second transistor are connected to a common load element, and the first and second load elements are formed as an integrated common load element.

Also, according to the present invention, there is provided an oscillator including a first oscillating circuit including a first oscillation transistor connected to a first resonance circuit; and a buffer transistor connected to the first oscillation transistor and a first load element and outputting a first oscillation signal having a first frequency; and a second oscillating circuit including a second oscillation transistor connected to a second resonance circuit and the first load element and outputting a second oscillation signal having a second frequency.

Further, according to the present invention, there is provided a mixer including, a first mixing circuit including a first transistor connected to a first load element and mixing at least two signals to output the resultant mixed signal from the first transistor; and a second mixing circuit including a second transistor connected to a second load element and mixing at least two signals to output the resultant mixed signal from the second transistor. The first transistor and the second transistor are connected a common load element, consisting of the first and second load elements.

According to the present invention, there is provided an oscillator comprising a plurality of transistors, collectors of which are connected to load elements; and a resonance circuit commonly connected to bases of said transistors. The transistors are connected in parallel, and oscillation signals are outputted from the collectors of the transistors.

According to the present invention, there is provided an oscillator including a plurality of pairs of transistors, collectors of which are respectively connected to load elements to form a Colpitz oscillation circuit; and a common resonance circuit connected between bases of the plurality of pairs of transistors. The plurality of pairs of transistors are connected in parallel, and a balanced output of oscillation signals is outputted from the collector of each transistor.

According to the present invention, there is provided an integrated oscillation circuit including, a connection terminal connected to an external resonance circuit and an input line of a mode switching signal which is set at a different level in response to an operation mode; an oscillation element; a bias terminal of which is connected to the connection terminal; a detection circuit detecting the level of said mode switching signal applied to the bias terminal of the oscillation element; and a switching circuit turning on or off a power source for driving the oscillation element in response to the level detected at the detection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and features and other objects and features of the present invention will be become apparently in more detail by the following description with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a television tuner circuit adapted to UHF/VHF;

FIG. 2 is a circuit diagram showing one example of the configuration of a general VHF local oscillator;

FIG. 3 is a circuit diagram showing one example of the configuration of a general UHF local oscillator;

FIG. 4 is a circuit diagram showing one example of the configuration of a general mixer;

FIG. 5 is a circuit diagram of an oscillator according to a first embodiment of the present invention;

FIG. 6 is a circuit diagram of another oscillator according to a second embodiment of the present invention;

FIG. 7 is a circuit diagram of another oscillator according to a third embodiment of the present invention;

FIGS. 8A and 8B are circuit diagrams of other oscillators according to fourth and fifth embodiments of the present invention;

FIG. 9 shows an oscillator according to a sixth embodiment of the present invention and a buffer circuit and a switch circuit used in the same;

FIG. 10 shows a circuit diagram of a UHF and VHF mixer according to a seventh embodiment of the present invention; and

FIG. 11 shows a diagram of a switching circuit of the oscillator according to an eighth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in detail referring to the drawings.

An explanation will be made first of a first embodiment of the present invention.

FIG. 5 is a circuit diagram showing a first embodiment of an oscillator according to the present invention applied to a frequency conversion circuit for a television tuner etc.

Namely, OSC_(U) denotes a UHF local oscillation circuit; T₁₁ to T₁₄ denote input/output terminals used as connection terminals with an external circuit etc.; RSN₃ denotes an external variable resonance circuit; C₁₂ and C₁₃ denote DC cutting capacitors; C₁₄ and C₁₅ denote capacitors for a positive feedback; and C₁₄ denotes a capacitor for connection, respectively.

Among these circuits, the UHF local oscillation circuit OSC_(U) is integrated together with a not illustrated UHF mixing circuit, a VHF mixing circuit and local oscillation circuit, and a common IF amplifier. The UHF local oscillation circuit OSC_(U) is connected via four input/output terminals T₁₁ to T₁₄ to the external variable resonance circuit RSN₃.

The local oscillation circuit OSC_(U) is constituted by a Colpitz oscillation circuit, consisting of oscillation npn-type transistors Q₃₁, Q₃₃, Q₃₅ and Q₃₇, npn-type transistors Q₃₂, Q₃₄, Q₃₆, and Q₃₈ functioning as loads, resistance elements R₃₁ and R₃₂, constant voltage sources V₁₁ to V₁₃ for biasing; and constant current sources I₁₁ and I₁₂.

The base of the oscillation transistor Q₃₁ is connected to the base of the oscillation transistor Q₃₅ and the input/output terminal T₁₁ and connected via the resistance element R₃₁ to the constant voltage source V₁₁. The emitter of the oscillation transistor Q₃₁ is connected to the input/output terminal T₁₂ and connected to the emitter of the oscillation transistor Q₃₅, the connection point of the emitter of the oscillation transistor Q₃₁ and the emitter of the oscillation transistor Q₃₅ is connected to the constant current source I₁₁, and other terminal of the constant current source I₁₁ is connected to the ground line GND. The collector of the oscillation transistor Q₃₁ is connected to the emitter of the transistor Q₃₂ for the load, and the output terminal O_(UT11) of the first differential type Colpitz oscillation circuit is constituted by the connection point of them. This output terminal O_(OT11) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₃₂ is connected to the constant voltage source V₁₂, and the collector is connected to the power source voltage V_(CC).

The base of the oscillation transistor Q₃₃ is connected to the base of the oscillation transistor Q₃₇ and the input/output terminal T₁₄ and connected via the resistance element R₃₂ to the constant voltage source V₁₁. The emitter of the oscillation transistor Q₃₃ is connected to the input/output terminal T₁₃ and connected to the emitter of the oscillation transistor Q₃₇, the connection point of the emitter of the oscillation transistor Q₃₃ and the emitter of the oscillation transistor Q₃₇ is connected to the constant current source I₁₂, and the constant current source I₁₂ is connected to the ground line GND. The collector of the oscillation transistor Q₃₃ is connected to the emitter of the transistor Q₃₄ for the load, and the output terminal O_(UT12) of the first differential operation type Colpitz oscillation circuit is constituted by the connection point of them. This output terminal O_(UT12) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₃₄ is connected to the constant voltage source V₁₂, and the collector is connected to the power source voltage V_(CC).

The base of the oscillation transistor Q₃₅ is connected, as mentioned before, to the base of the oscillation transistor Q₃₁ and connected via the input/output terminal T₁₁ and the resistance element R₃₁ to the constant voltage source V₁₁. The emitter of the oscillation transistor Q₃₅ is connected, as mentioned before, to the emitter of the oscillation transistor Q₃₁ and connected to the input/output terminal T₁₂, and the connection point of the emitter of the oscillation transistor Q₃₅ and the emitter of the oscillation transistor Q₃₁ is connected to the constant current source I₁₁. The collector of the oscillation transistor Q₃₅ is connected to the emitter of the load transistor Q₃₆, and the output terminal O_(UT13) of the second differential operation type Colpitz oscillation circuit is constituted by the connection point of them. This output terminal O_(UT13) is connected to for example a not illustrated PLL circuit.

The base of the load transistor Q₃₆ is connected to the constant voltage source V₁₃, and the collector is connected to the line of the power source voltage V_(CC).

The base of the oscillation transistor Q₃₇ is connected, as mentioned before, to the base of the oscillation transistor Q₃₃ and connected via the input/output terminal T₁₄ and the resistance element R₃₂ to the constant voltage source V₁₁. The emitter of the oscillation transistor Q₃₇ is connected, as mentioned before, to the emitter of the oscillation transistor Q₃₃ and connected to the input/output terminal T₁₃, and the connection point of the emitter of the oscillation transistor Q₃₇ and the emitter of the oscillation transistor Q₃₃ is connected to the constant current source I₁₂. The collector of the oscillation transistor Q₃₇ is connected to the emitter of the load transistor Q₃₈, and the output terminal O_(UT14) of the second differential type Colpitz oscillation circuit is constituted by the connection point of them. This output terminal O_(UT14) can be connected to for example a not illustrated PLL circuit.

The base of the load transistor Q₃₈ is connected to the constant voltage source V₁₃, and the collector is connected to the line of the power source voltage V_(CC).

The external variable resonance circuit RSN₃ is constituted by connecting a capacitor C₁₁ in parallel to a serial circuit of a variable capacitance diode CV₃ and a coil L₁₀.

The connection point of the coil L₁₀ of the external variable resonance circuit RSN₃ and the capacitor C₁₁ is connected via a DC cutting capacitor C₁₃ and the input/output terminal T₁₁ to the base of the oscillation transistors Q₃₁ and Q₃₅, and the connection point of the anode of the variable capacitance diode CV₃ and the capacitor C₁₁ is connected via the DC cutting capacitor C₁₃ and the input/output terminal T₁₄ to the bases of the oscillation transistors Q₃₃ and Q₃₇.

Also, a positive feedback capacitor C₁₄ is connected between the connection point of the capacitor C₁₂ and input/output terminal T₁₁ and the input/output terminal T₁₂, and a positive feedback capacitor C₁₅ is connected between the connection point of the capacitor C₁₃ and input/output terminal T₁₄ and the input/output terminal T₁₃.

Further, a coupling capacitor C₁₆ is connected to the connection point of the capacitor C₁₄ and the input/output terminal T₁₂ and the connection point of the capacitor C₁₅ and the input/output terminal T₁₃ i.e., between the emitters of the oscillation transistors Q₋ and Q₃₅ and between the emitters of the oscillation transistors Q₃₃ and Q₃₇.

The local oscillation circuit OSC_(U) is subjected to a positive feedback via the input/output terminals T₁₁ and T₁₂, and T₁₃ and T₁₄ by the capacitors C₁₄ and C₁₅ connected between the base and emitter of the oscillation transistors Q₃₁ and Q₃₃. It oscillates at the resonance frequency of the external variable resonance circuit RSN₃ connected to the bases of the oscillation transistors Q₃₁ and Q₃₅ and Q₃₃ and Q₃₇ and outputs the local oscillation frequency signals S_(LU1) and S_(LU2) at the predetermined frequency from the output terminals O_(UT11) and O_(UT12) and O_(UT13) and O_(UT14) to the not illustrated UHF mixing circuit MIX_(U) and the PLL circuit, respectively.

Note that, the oscillation transistors Q₃₁ and Q₃₃ constituting the first differential operation type Colpitz oscillation circuit are mutually connected at their respective bases via the external variable resonance circuit RSN₃ and accordingly perform the oscillation operation with out of phases to each other.

Similarly, the oscillation transistors Q₃₅ and Q₃₇ constituting the second differential operation type Colpitz oscillation circuit are mutually connected at respective bases via the external variable resonance circuit RSN₃ and accordingly perform the oscillation operation with out of phases to each other.

Accordingly, local oscillation frequency signals S_(LU1) and S_(LU2) having out of phases to each other are output from the output terminals O_(UT11) and O_(UT12) and O_(UT13) and O_(UT14).

As mentioned above, the present oscillator comprises as basic constituent elements two differential type Colpitz oscillation circuits using two pairs of oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ and has a structure in which the base and emitter of the oscillation transistors Q₃₁ and Q₃₅ are connected, the base and emitter of the oscillation transistors Q₃₃ and Q₃₇ are connected, and the collectors of the respective oscillation transistors Q₃₁, Q₃₃, Q₃₅, and Q₃₇ are separated from each other.

The Colpitz oscillation circuit of the present embodiment is basically an oscillation circuit grounded at its collector. The collector-grounded oscillation is oscillation between the emitter and base of the transistor in other words.

Accordingly, if the base and emitter of the transistor are commonly connected as in the oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ of the present oscillator, the oscillation transistor will be increased.

This is equivalent to the reduction of base resistors deteriorating the high frequency characteristic of the transistor. The oscillation strength is enhanced and the performance becomes better.

Also, even if the bases and emitters of the oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ are commonly connected, the respective collectors are separated as mentioned above, and therefore even if for example the output terminals O_(UT11) and O_(UT12), are connected to the UHF mixing circuit MIX_(U) and the output terminals O_(UT13) and O_(UT14) are connected to the PLL circuit, the signal will not directly go around from the mixing circuit MIX_(U) to the PLL circuit.

Further, the output amplitudes of the oscillation signals S_(LU1) and S_(LU2) are determined by the product between the collector current of the oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ and the load impedance.

The collector current of oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ flows while the current from the constant current source I₁₁ is divided in proportion to the size of the oscillation transistors Q₃₁ and Q₃₃ and flows while the current by the constant current source I₁₂ is divided in proportion to the size of the oscillation transistors Q₃₅ and Q₃₇, and therefore by appropriately selecting the size ratio of the oscillation transistors and the value of the current source, the output amplitude of the oscillation signals S_(LU1) and S_(LU2) can be freely set up.

As explained above, according to the present embodiment, there are advantages such that a balanced output of a plurality of oscillation signals can be extracted with any amplitude by a simple circuit without an influence exerted upon the oscillation characteristic and a reduction of power consumption can be achieved.

Note that, in the present embodiment, transistors Q₃₂ and Q₃₄ and Q₃₆ and Q₃₈, are used as the load elements, but the elements are not restricted to them, and there arises no problem even if a resistance element or diode is used.

The load element converts the collector current of the oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ to voltage. Further, the Colpitz oscillation circuit of the present embodiment is basically a collector-grounded oscillation circuit as mentioned before. Therefore, the collectors of the oscillation transistors Q₃₁ and Q₃₃ and Q₃₅ and Q₃₇ are grounded at a low impedance, and there is a function of lowering the output impedance of the oscillation signal output, and therefore it is also possible to use a resistance element so far as the impedance is low.

Also, in the present embodiment, an explanation was made using a differential operation type oscillator using a plurality of pairs of oscillation transistors as an example, but needless to say effects similar to the effects mentioned above are obtained even if the oscillation transistor is not a differential operation type and has a so-called single configuration comprising only the oscillation transistors Q₃₁ and Q₃₃ or only Q₃₅ and Q₃₇ in FIG. 5.

Next, a second embodiment of the present invention will be explained.

FIG. 6 is a circuit diagram showing the second embodiment of the oscillator according to the present invention.

The present embodiment differs from the above-described first embodiment in that resistance elements R₃₇ and R₃₈, having a low impedance are used in place of the use of the npn-type transistors as the load elements of the oscillation transistors Q₃₁ and Q₃₃.

In the present embodiment, a series-connected npn-type transistor Q₄₉ and constant current source I₂₃ and npn-type transistor Q₅₀ and constant current source I₂₄ are connected in parallel between the power source voltage V_(CC) and the ground line GND, the connection point between the collector of the oscillation transistor Q₄₁ and the resistance element R₃₇ is connected to the base of the npn-type transistor Q₄₉, the connection point between the collector of the oscillation transistor Q₄₃ and the resistance element R₃₈ is connected to the base of the npn-type transistor Q₅₀, the connection point between the emitter of the npn-type transistor Q₄₉ and the constant current source I₂₃ is made the output terminal O_(UT16), and the connection point between the emitter of the npn-type transistor Q₅₀ and the constant current source I₂₄ is made the output terminal O_(UT17), whereby a plurality of outputs are obtained.

Also in the oscillator according to the present embodiment having such a configuration, effects similar to the effects of the above-mentioned first embodiment can be obtained.

Note that, in addition to the above-described configuration, for example, npn-type transistors are respectively cascade-connected between the connection point between the load resistance element R₃₇ and output terminal O_(UT16) and the collector of the oscillation transistor Q₄₁ and between the connection point between the load resistance element R₃₈ and output terminal O_(UT17) and the collector of the oscillation transistor Q₄₃, and the bases of the cascade-connected npn-type transistors are grounded, whereby the output terminal O_(UT16) and O_(UT17) side can be retained stably at a low impedance.

An explanation will be made next of a third embodiment of the present invention.

FIG. 7 is a circuit diagram showing the third embodiment of the oscillator according to the present invention.

The present embodiment differs from the above-described first embodiment in that diodes D₁ and D₂ and the resistance elements R₄₅ and R₄₆ are used instead of use of the npn-type transistors as the load elements of the oscillation transistors Q₃₁, Q₃₃, Q₃₅, and Q₃₇.

Concretely, in FIG. 7, the diodes D₁ and D₂ are used as the load elements of the oscillation transistors Q₅₁ and Q₅₃, the cathode of the diode D₁ is connected to the collector of the oscillation transistor Q₅₁, and the cathode of the diode D₂ is connected to the collector of the oscillation transistor Q₅₃.

Also, anodes of the diodes D₁ and D₂ are connected to each other, and the connection point between them is connected via the resistance element R₄₇ to the power source voltage V_(CC) and connected to one electrode of the capacitor C₃₇. The other electrode of the capacitor C₃₇ is connected to the ground line GND.

Further, emitter resistance elements R₄₉ and R₅₀ are connected to the oscillation transistors Q₅₁ and Q₅₃, respectively.

In the case where the load element is the diode, a distortion is increased at a large input in comparison with the case where the load element is a resistance element, and therefore these emitter resistance elements R₄₉ and R₅₀ are inserted for a purpose of suppressing this distortion.

Also, as the load element of the oscillation transistors Q₅₅ and Q₅₇, the resistance elements R₄₅ and R₄₆ are used. One end of the resistance element R₄₅ is connected to the collector of the oscillation transistor Q₅₅, and one end of the resistance element R₄₆ is connected to the collector of the oscillation transistor Q₅₇.

Also, the other ends of the resistance elements R₄₅ and R₄₆ are connected to each other, and the connection point between them is connected via the resistance element R₄₈ to the line of the power source voltage V_(CC) and connected to one electrode of the capacitor C₃₈. The other electrode of the capacitor C₃₈ is connected to the ground line GND.

Note that, the resistance element is not connected to the emitter of the oscillation transistors Q₅₅ and Q₅₇ in which the load element is the resistance element since the resistance element which is the load element moderates the distortion.

In such a configuration, the resistance element R₄₇ and capacitor C₃₇ and the resistance element R₄₈ and capacitor C₃₈ have a function of a low pass filter and reduce the high frequency of the oscillation.

The rest of the configuration is similar to the first embodiment of the present invention. Also in the oscillator according to the present embodiment, effects similar to the effects of the above-mentioned first embodiment can be obtained.

Next, an explanation will be made of fourth and fifth embodiments of the present invention.

FIGS. 8A and 8B are circuit diagrams showing the fourth and fifth embodiments of the oscillator according to the present invention.

The present embodiment differs from the above-described first to third embodiments in that the configuration is made so that, instead of two differential outputs being obtained using two pairs of oscillation transistors, n (n is an integer of 3 or more) pairs (2×n) or n oscillation transistors are used to obtained n outputs.

In FIG. 8, FIG. 8-A shows a differential operation type n-output oscillator; and FIG. 8B shows a single type n-output oscillator.

Concretely, in FIG. 8A, the oscillation transistors Q₆₁, Q₆₂, and Q₆₃ are commonly connected to each other at their bases, and the bases thereof are connected via the input/output terminals T₂₆ and the resistor R₅₁ to the constant voltage source V₁₉. Also, the emitters of the oscillation transistors Q₆₁, Q₆₂, and Q₆₃ are commonly connected to each other and are connected to the input/output terminal T₂₇ and the constant current source I₃₁, and the constant current source I₃₁ is connected to the ground line GND. The collector of the oscillation transistor Q₆₁ is connected to the cathode of the load diode, and the first output terminal O_(UT25) is constituted from the connection point between them.

The collectors of the oscillation transistors Q₆₂ and Q₆₃ are connected to the cathode of the load diode in the same way as the transistor Q₆₁, respectively, and a second output terminal O_(UT23) and a third output terminal O_(UT21) are constituted from the connection point between them. The anode side of these load diodes is connected to the line of the power source voltage V_(CC).

The oscillation transistors Q₆₄, Q₆₅, and Q₆₆ are commonly connected to each other at their bases, and the bases thereof are connected via the input/output terminals T₂₉ and the resistor R₅₂ to the constant voltage source V₁₉. Also, the emitters of the oscillation transistors Q₆₄, Q₆₅, and Q₆₆ are commonly connected to each other and are connected to the input/output terminal T₂₈ and the constant current source I₃₂, and the constant current source I₃₂ is connected to the ground line GND. The collector of the oscillation transistor Q₆₆ is connected to the cathode of the load diode, and the first output terminal O_(UT26) is constituted from the connection point between them.

The collectors of the oscillation transistors Q₆₅ and Q₆₄ are connected to the cathode of the load diode in the same way as the transistor Q₆₆, respectively, and a second output terminal O_(UT24) and a third output terminal O_(UT22) are constituted from the connection point between them. The anode side of these load diodes is connected to the line of the power source voltage V_(CC).

According to the oscillator according to the present embodiment having such a configuration, in the same way as the effect of the above-mentioned first embodiment, three sets of differential outputs can be obtained. Note that, in the present embodiment, a case of three sets was indicated, but it is true also for the case of four sets or more.

Also, in the present embodiment, a case where the load element was the diode was used, but there is no problem even if it is a resistor or an npn-type transistor as in the first to third embodiments.

An explanation will be made next of FIG. 8B. The oscillation transistors Q₆₇, Q₆₈, and Q₆₉ are commonly connected to each other at their bases, and the bases thereof are connected via the input/output terminals T₃₁ and the resistor R₅₄ to the constant voltage source V₂₀. Also, the emitters of the oscillation transistors Q₆₇, Q₆₈, and Q₆₉ are commonly connected to each other and are connected to the input/output terminal T₃₂ and the constant current source I₃₄, and the constant current source I₃₄ is connected to the ground line GND. The collector of the oscillation transistor Q₆₇ is connected to the cathode of the load diode, and the first output terminal O_(UT29) is constituted from the connection point between them.

The collectors of the oscillation transistors Q₆₈ and Q₆₉ are connected to the cathode of the load diode in the same way as Q₆₇, respectively, and a second output terminal O_(UT27) and a third output terminal O_(UT26) are constituted from the connection point between them. The anode side of these load diodes is connected to the line of the power source voltage V_(CC).

The external variable resonance circuit is connected between the input/output terminal T₃₁ and the ground via the DC cutting capacitor. A positive feedback capacitor is connected between the input/output terminals T₃₁ and T₃₂, and further the ground capacitor is connected between the T₃₂ and the ground.

By the above configuration, the circuit operates as a Colpitz oscillation circuit.

Also, in the present embodiment, a case where the load element is a diode is mentioned, but there is no problem even if it is a resistor or an npn-type transistor as in the first to third embodiments.

In this way, in the present embodiment, three or more outputs can be obtained, and therefore an oscillator of a high general usefulness can be realized.

As explained above, according to the present invention, a balanced output of a plurality of oscillation signals can be extracted with any amplitude by a simple circuit without an influence exerted upon the oscillation characteristic, and an oscillator of a high general usefulness which can achieve the reduction of the consumption of electric power can be realized.

Art explanation will be made next of a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram showing one embodiment of a UHF/VHF oscillator according to the present invention applied to an integrated frequency conversion circuit for a television tuner.

A VHF local oscillation circuit OSC_(V) is constituted by oscillation npn-type transistors Q₇₁ and Q₇₂ constituting a positive feedback differential amplifier type oscillation circuit; a biasing constant voltage source V₂₁ of the oscillation npn-type transistors Q₇₁ and Q₇₂ ; resistance elements R₆₁, R₆₂, and R₆₃ ; and a constant current source I₄₀.

The base of the oscillation transistor Q₇₁ is connected to the input/output terminal T₄₁ and connected via the resistance element R₆₁ to the constant voltage source V₂₁ and further connected to the base of the npn-type transistor Q₇₄ of the output buffer BUF_(V). The emitter of the oscillation transistor Q₇₁ is connected to the constant current source I₄₀, and the other terminal of the constant current source I₄₀ is grounded. The collector of the oscillation transistor Q₇₁ is connected to the line of the power source voltage V_(CC).

The base of the oscillation transistor Q₇₂ is connected to the input/output terminal T₄₃ and connected via the resistance element R₆₂ to the constant voltage source V₂₁ and further connected to the base of the npn-type transistor Q₇₃ of the output buffer BUF_(V). The emitter of the oscillation transistor Q₇₂ is connected to the constant current source I₄₀, and the collector is connected to the input/output terminal T₄₂. Also, the resistance element R₆₃ is connected between the collector of the oscillation transistor Q₇₂ and the line of the power source voltage V_(CC).

The external variable resonance circuit RSN₆ is constituted by the variable capacitance capacitor CV₆ and the coil L₁₃ which are connected in parallel.

The connection point between one end of the coil L₁₃ of the external variable resonance circuit RSN₆ and one electrode of the variable capacitance capacitor CV₆ is grounded. The connection point between the other end of the coil L₁₃ and the other electrode of the variable capacitance capacitor CV₆ is connected via the capacitor C₄₁ and the input/output terminal T₄₁ to the base of the oscillation transistor Q₇₁ and connected via the capacitor C₄₂ and the input/output terminal T₄₂ to the collector of the oscillation transistor Q₇₂.

Also, one electrode of the capacitor C₄₃ is connected to the input/output terminal T₄₃, and the other electrode of the capacitor C₄₃ is grounded.

The VHF local oscillation circuit OSC_(V) is subjected to a positive feedback by the externally attached capacitor C₄₁ connected via the input/output terminals T₄₂ and T₄₁ to the base of the oscillation transistor Q₇₁. It oscillates at the resonance frequency of the external variable resonance circuit RSN₆ and outputs to the output buffer BUF_(V).

The output buffer BUF_(V) is constituted by npn-type transistors Q₇₃ and Q₇₄, the load resistance elements R₆₄ to R₆₆, resistance elements R₆₇ to R₇₀, and a constant current source I₄₁.

The base of the transistor Q₇₃ is connected to the base of the oscillation transistor Q₇₂ of the local oscillation circuit OSC_(V) as mentioned above, the emitter thereof is connected via the series-connected resistance elements R₆₇ and R₆₈ to the constant current source I₄₁, and the other terminal of the constant current source I₄₁ is grounded. The collector of the transistor Q₇₃ is connected via the series-connected load resistance elements R₄₅ and R₆₈ to the line of the power source voltage V_(CC).

Note that, the output terminal O_(UT33) of the VHF local oscillation circuit is constituted by the connection point between the resistance element R₆₇ and the resistance element R₆₈. The output terminal O_(UT33) of this is connected to the not illustrated integrated VHF mixing circuit MIX_(V).

Also, the output terminal O_(UT31) of the oscillation signal to the not illustrated PLL circuit is constituted by the connection point between the collector of the transistor Q₇₃ and the load resistance element R₆₅.

The base of the transistor Q₇₄ is connected to the base of oscillation transistor Q₇₁ of the local oscillation circuit OSC_(V) as mentioned above, and the emitter thereof is connected via the series-connected resistance elements R₆₉ and R₇₀ to the constant current source I₄₁. The collector of the transistor Q₇₄ is connected via the load resistance element R₆₆ to the connection point between the series-connected load resistance elements R₆₅ and R₆₄.

Note that, the output terminal O_(UT34) of the VHF local oscillation circuit is constituted by the connection point between the resistance element R₆₉ and the resistance element R₇₀. The output terminal O_(UT34) of this is connected to the not illustrated VHF integrated mixing circuit MIX_(V).

Also, the output terminal O_(UT32) of the oscillation signal to the not illustrated PLL circuit is constituted by the connection point between the collector of the transistor Q₇₄ and the load resistance element R₆₆.

Art explanation will be made next of the UHF local oscillation circuit OSC_(U). It is constituted by oscillation npn-type transistors Q₇₈, Q₇₉, Q₈₁, and Q₈₂ which constitute a differential operation type Colpitz oscillation circuit; load npn-type transistors Q₈₀ and Q₈₃ ; resistance elements R₇₄ and R₇₅ ; biasing constant voltage sources V₂₂ and V₂₃ ; and constant current sources I₄₂ and I₄₃.

The base of the oscillation transistor Q₇₈ is connected to the base of the oscillation transistor Q₇₉ and the input/output terminal T₄₆ and connected via the resistance element R₇₄ to the constant voltage source V₂₃. The emitter of the oscillation transistor Q₇₈ is connected to the input/output terminal T₄₇ and connected to the emitter of the oscillation transistor Q₇₉, the connection point between the emitter of the oscillation transistor Q₇₈ and the emitter of the oscillation transistor Q₇₉ is connected to the constant current source I₄₂, and the constant current source I₄₂ is connected to the ground line GND. The collector of the oscillation transistor Q₇₈ is connected to the emitter of the load transistor Q₈₀, and the output terminal O_(UT35) of the first differential operational type Colpitz oscillation circuit is constituted by the connection point between them. This output terminal O_(UT35) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₈₀ is connected to the constant voltage source V₂₂, and the collector is connected to the line of the power source voltage V_(CC).

The collector of the oscillation transistor Q₇₉ is connected to the output terminal O_(UT31) to the PLL circuit which is the connection point between the collector of the transistor Q₇₃ of the output buffer BUF_(V) of the VHF local oscillation circuit OSC_(V) and the load resistance element R₆₅.

The base of the oscillation transistor Q₈₂ is connected to the base of the oscillation transistor Q₈₁ and the input/output terminal T₄₉ and connected via the resistance element R.sub. 75 to the constant voltage source V₂₃. The emitter of the oscillation transistor Q₈₂ is connected to the input/output terminal T₄₈ and connected to the emitter of the oscillation transistor Q₈₁, the connection point between the emitter of the oscillation transistor Q₈₂ and the emitter of the oscillation transistor Q₈₂ is connected to the constant current source I₄₃, and the constant current source I₄₃ is connected to the ground line GND. The collector of the oscillation transistor Q₈₂ is connected to the emitter of the load transistor Q₈₃, and the output terminal O_(UT36) of the first differential operation type Colpitz oscillation circuit is constituted by the connection point between them. This output terminal O_(UT36) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₈₃ is connected to the constant voltage source V₂₂, and the collector is connected to the line of the power source voltage V_(CC).

The collector of the oscillation transistor Q₇₉ is connected to the output terminal O_(UT32) to the PLL circuit which is the connection point between the collector of the transistor Q₇₄ of the output buffer BUF_(V) of the VHF local oscillation circuit OSC_(V) and the load resistance element R₆₆.

In this way, the UHF local oscillation circuit OSC_(U) commonly uses the load elements of the oscillation transistors Q₇₉ and Q₈₁ and the load resistance elements R₆₄ to R₆₆ of the output buffer BUF_(V) of the VHF local oscillation circuit OSC_(V) and commonly uses also the output terminals O_(UT31) and O_(UT32) to the PLL circuit.

The external variable resonance circuit RSN₇ is constituted by connecting a capacitor C₄₄ in parallel to a serial circuit of a variable capacitance diode C₇ and the coil L₁₄.

The connection point between the coil L₁₄ of the external variable resonance circuit RSN₇ and the capacitor C₄₄ is connected via the DC cutting capacitor C₄₅ to the input/output terminal T₄₆ to the bases of the oscillation transistors Q₇₈ and Q₇₉, and the connection point between the anode of the variable capacitance diode CV₇ and the capacitor C₄₄ is connected via the DC cutting capacitor C₄₆ and the input/output terminal T₄₉ to the bases of the oscillation transistors Q₈₁ and Q₈₂.

Also, a positive feedback capacitor C₄₇ is connected between the connection point between the capacitor C₄₅ and input/output terminal T₄₆ and the input/output terminal T₄₇, and a positive feedback capacitor C₄₉ is connected between the connection point between the capacitor C₄₆ and input/output terminal T₄₉ and the input/output terminal T₄₈.

Further, a coupling capacitor C₄₈ is connected between the connection point between the capacitor C₄₇ and the input/output terminal T₄₇ and the connection point between the capacitor C₄₉ and the input/output terminal T₄₈ (between the emitters of the oscillation transistors Q₇₈ and Q₇₉ and the emitters of the oscillation transistors Q₈₁ and Q₈₂).

The UHF local oscillation circuit OSC_(U) is subjected to a positive feedback by the externally attached capacitors C₄₇ and C₄₉ connected between the bases and emitters of the oscillation transistors Q₇₈ and Q₇₉ and Q₈₂ and Q₈₂ via the input/output terminals T₄₆, T₄₇, T₄₈, and T₄₉. It is oscillated by the resonance frequency of the external variable resonance circuit RSN₇ connected to respective bases of the oscillation transistors Q₇₈ and Q₇₉ and Q₈₁ and Q₈₂ and outputs the local oscillation frequency signal S_(LU) at the predetermined frequency from the output terminals O_(UT35) and O_(UT36) to the UHF mixing circuit MIX_(V).

Note that, the oscillation transistors Q₇₈ and Q₇₉ and Q₈₁ and Q₈₂ constituting the differential operation type Colpitz oscillation circuit perform oscillation operations of out of phases to each other since the respective bases are mutually connected via the external variable resonance circuit RSN₇.

Accordingly, local oscillation frequency signals having out of phases to each other are output from the output terminals O_(UT35) and O_(UT36).

The switching circuit SW is constituted by switching operation npn-type transistor Q₇₆ and Q₇₇ and the resistance elements R₇₃, R₇₂, and R₇₆.

The base of the switching transistor Q₇₆ is connected via the resistance element R₇₃ to the collector of the switching transistor Q₇₇, the emitter is grounded, and the collector is connected to the not illustrated UHF system current source.

The base of the switching transistor Q₇₇ is connected via the R₇₆ to the switching terminal T₄₄, the emitter is grounded, the connection point between the collector and the resistance element R₇₃ is connected via the high resistance element R₇₂, to the line of the power source voltage V_(CC), and the connection point between the collector and the resistance element R₇₃ and the connection point with the high resistance element R₇₂ is connected to the not illustrated VHF system current source.

Art explanation will be made next of a UHF and VHF mixing circuit and an IF amplifier using FIG. 10.

The VHF mixing circuit MIX_(V) is constituted by npn-type transistors Q₈₄ to Q₈₉, resistance elements R₈₀ to R₈₂ and constant current sources I₄₅ and I₄₆.

The base of the transistor Q₈₄ is connected to the output of the VHF local oscillation circuit OSC_(V) and the base of the transistor Q₈₇. The emitter of the transistor Q₈₄ is connected to the emitter of the transistor Q₈₅ and the collector of the transistor Q₈₈. The collector of the transistor Q₈₄ is connected via the resistance element R₈₀ to the line of the power source voltage V_(CC), and the connection point between the collector and the resistance element R₈₀ is connected to the collector of the transistor Q₈₆ and further connected to one input of the IF amplifier AMP_(IF).

The base of the transistor Q₈₅ is connected to the output of the VHF local oscillation circuit OSC_(V) and the base of the transistor Q₈₆, and the collector is connected to the other input of the IF amplifier AMP_(IF).

The emitter of the transistor Q₈₆ is connected to the emitter of the transistor Q₈₇ and the collector of the transistor Q₈₉. The collector of the transistor Q₈₆ is connected to one input of the IF amplifier AMP_(IF).

The collector of the transistor Q₈₇ is connected via the resistance element R₈₁ to the line of the power source voltage V_(CC), and the connection point between the collector and the resistance element R₈₁ is connected to the collector of the transistor Q₈₅ and further connected to the other input of the IF amplifier AMP_(IF).

The base of the transistor Q₈₈ is connected to the input line of the RF signal RF_(V) of VHF, the emitter is connected to the constant current source I₄₅, and the other terminal of the constant current source I₄₅ is grounded.

The base of the transistor Q₈₉ is connected to the input line of the RF signal RF_(V) of VHF, the emitter is connected to the constant current source I₄₆, and the constant current source I₄₆ is grounded.

Also, the resistance element R₈₂ is connected between the emitter of the transistor Q₈₈ and the emitter of the transistor Q₈₉.

This VHF mixing circuit MIX_(V) mixes the local oscillation frequency signal S_(LV) by the local oscillation circuit OSC_(V) at the frequency higher than the frequency of the video image carrier wave signal RF_(V) of the VHF band width of the selected channel by the predetermined frequency, for example, 58.75 MHz, and extracts the intermediate frequency signal IF_(V), which is the frequency of the difference therebetween, and outputs the same to IF amplifier AMP_(IF) commonly used for UHF and VHF.

The UHF mixing circuit MIX_(U) is constituted by npn-type transistors Q₉₀ to Q₉₅, a resistance element R₈₃, and constant current sources I₄₇ and I₄₈.

The base of the transistor Q₉₀ is connected to the output of the UHF local oscillation circuit OSC_(U) and the base of the transistor Q₉₃. The emitter of the transistor Q₉₀ is connected to the emitter of the transistor Q₉₁ and the collector of the transistor Q₉₄. The collector of the transistor Q₉₀ is connected to the connection point between the collector of the transistor Q₈₄ of the VHF mixing circuit MIX_(V) and the resistance element R₈₀, the collector of the transistor Q₈₆, and one input of the IF amplifier AMP_(IF).

The base of the transistor Q₉₁ is connected to the output of the VHF local oscillation circuit OSC_(U) and the base of the transistor Q₉₂. The collector of the transistor Q₉₁ is connected the connection point between the collector of the transistor Q₈₇ of the VHF mixing circuit MIX_(V) and the resistance element R₈₁, the collector of the transistor Q₈₅, and the other input of the IF amplifier AMP_(IF).

The emitter of the transistor Q₉₂ is connected to the emitter of the transistor Q₉₃ and the collector of the transistor Q₉₅. The collector of the transistor Q₉₂ is connected to the connection point between the collector of the transistor Q₈₄ of the VHF mixing MIX_(V) and the resistance element R₈₀, the collector of the transistor Q₈₆, and one input of the IF amplifier AMP_(IF).

The collector of the transistor Q₉₃ is connected to the connection point between the collector of the transistor Q₈₇ of the VHF mixing MIX_(V) and the resistance element R₈₁, the collector of the transistor Q₈₅, the collector of the transistor Q₉₁, and the other input of the IF amplifier AMP_(IF).

The base of the transistor Q₉₄ is connected to the input line of the signal RF_(U), the emitter is connected to the constant current source I₄₇, and the other terminal of the constant current source I₄₇ is grounded.

The base of the transistor Q₉₅ is connected to the input line of the signal RF_(U), the emitter is connected to the constant current source I₄₈, and the other terminal of the constant current source I₄₈ is grounded.

Also, the resistance element R₈₃ is connected between the emitter of the transistor Q₉₄ and the emitter of the transistor Q₉₅.

In this way, the UHF mixing circuit MIX_(U) commonly uses the load resistance elements R₈₀ and R₈₁ of the VHF mixing circuit MIX_(V) as the load elements.

This UHF mixing circuit MIX_(U) mixes the local oscillation frequency signal S_(LU) by the local oscillation circuit OSC_(U) at the frequency higher than the frequency of the video image carrier wave signal RF_(U) of the UHF band width of the selected channel by a predetermined frequency, for example, 58.75 MHz, extracts the intermediate frequency signal IF_(U), which is the frequency of the difference therebetween, and outputs the same to IF amplifier AMP_(IF) commonly used for UHF and VHF.

An explanation will be made next of the operation by the above-described configuration.

At the VHF operation, a UHF/VHF mode changing signal S_(SW) of the low level "0 V" is input to the switching terminal T₄₄ by for example an external control system. Alternatively, the switching terminal T₄₄ is made open.

By this, the base potential of the switching transistor Q₇₇ becomes "0 V", and therefore the switching transistor Q₇₇ is retained in the OFF state.

Accordingly, the current generated via the high resistance element R₇₂ is supplied to the VHF current source. Along with this, the driving current is supplied to the VHF local oscillation circuit OSC_(V) and mixing circuit MIX_(V).

Also, the current generated via the high resistance element R₇₂ is applied via the resistance element R₇₃ as the predetermined signal voltage to the base of the switching transistor Q₇₆.

By this, the switching transistor Q₇₆ becomes ON in state, and the UHF system current source connected to the collector thereof becomes OFF. Accordingly, the driving current is not supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

Accordingly, at the VHF operation mode, where a VHF broadcast is received, only the VHF local oscillation circuit OSC_(V) and mixing circuit MIX_(V) are driven, a local oscillation frequency signal S_(LV) having a frequency higher than the frequency of the video image carrier wave signal RF_(V) of the channel selected from the VHF local oscillation circuit OSC_(V) by the predetermined frequency is output from the output buffer BUF_(V) to the mixing circuit MIX_(V).

By this, the mixing circuit MIX_(V) mixes the video image carrier wave signal RF_(V) of the selected channel and the local oscillation frequency signal S_(LV), extracts the intermediate frequency signal IF_(V), which is the frequency of the differential thereof, and output this to the IF amplifier AMP_(IF) commonly used for UHF and VHF.

At the IF amplifier AMP_(IF), the predetermined amplification function is carried out, whereby the IF output of VHF is obtained.

Contrary to this, at the UHF operation, a UHF/VHF mode changing signal S_(SW) of a high level of "9 V", the same level as that of the power source voltage V_(CC), is applied to the switching terminal T_(SW) by for example the external control system.

By this, the base potential of the switching transistor Q₇₇ becomes the high level, and therefore the switching transistor Q₇₇ is retained in the ON state.

Accordingly, the current generated via the high resistance element R₇₂ is passed through the switching transistor Q₇₇, not supplied to the VHF current source, and the collector side is retained at "0 V" at the switching transistor Q₇₂. Along with this, the driving current is not supplied to the VHF local oscillation circuit OSC_(V), output buffer BUF_(V), and mixing circuit MIX_(V).

Also, since the collector side of the switching transistor Q₇₇ is retained at "0 V", the base potential of the switching transistor Q₇₆ becomes "0 V", and therefore the switching transistor Q₇₆ is retained in the OFF state.

By this, the UHF system current source connected to the collector of the switching transistor Q₇₆ is turned ON. Accordingly, the driving current is supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

Accordingly, at the UHF operation mode, when a UHF broadcast is received, only the UHF local oscillation circuit OSC_(U) and mixing circuit MIX_(U) are driven, the local oscillation frequency signal S_(LU) at the frequency higher than the frequency of the video image carrier wave signal RF_(U) Of the selected channel by a predetermined frequency is output from the oscillation transistors Q₇₈ and Q₇₉ with collectors which are connected to the load resistance elements R₆₅ and R₆₆ of the VHF output buffer BUF_(V) to the mixing circuit MIX_(U).

At this time, as mentioned above, the driving current is not supplied to the VHF local oscillation circuit OSC_(V) and output buffer BUF_(V), and therefore no influence is exerted upon the oscillation operation of the UHF local oscillation circuit OS_(U).

By this, the mixing circuit MIX_(U) mixes the video image carrier wave signal RF_(U) of the selected channel and the local oscillation frequency signal S_(LU), extracts the intermediate frequency signal IF_(U), which is the frequency of the difference therebetween, and outputs this to the IF amplifier AMP_(IF) commonly used for the UHF and VHF.

At the IF amplifier AMP_(IF), the predetermined amplification function is carried out, whereby the IF output of UHF is obtained.

Also, irrespective of the UHF/VHF operation, an oscillation signal in accordance with the operation mode is output from the output terminals O_(UT31) and O_(UT32), which are middle points of connection between the collectors of the transistors Q₇₃ and Q₇₄, of the output buffer BUF_(V) of the VHF local oscillation circuit OSC_(V) and the load resistance elements R₆₅ and R₆₆ to the PLL circuit.

As explained above, according to the present embodiment, as the load element of the oscillation transistors Q₇₉ and Q₈₁ in the UHF local oscillation circuit OSC_(U), the configuration is made so that the load resistance elements R₆₄ to R₆₆ of the output block BUF_(V) of the VHF local oscillation circuit OSC_(V) which are not simultaneously driven are commonly used and, also the output terminals O_(UT31) and O_(UT32) to the PLL circuit are commonly used. Therefore, a reduction of the number of elements can be achieved and the number of the outputs to the PLL circuit, which basically has one input, becomes one, it becomes unnecessary to provide a switching circuit, and so on. Therefore, there is an advantage such that the connection to the PLL circuit becomes easy, and the increase of the number of element can be suppressed.

Also, since the configuration is made so that the circuits are not simultaneously driven and so that the load elements of the VHF mixing circuit MIX_(V) and UHF mixing circuit MIX_(U) which output the intermediate frequency signals IF_(V) and IF_(U) obtained as a result of mixing to the commonly used IF amplifier AMP_(IF) are commonly used as the load resistance elements RM₈₀ and RM₈₁ of the VHF mixing circuit MIX_(V), there are advantages such that the reduction of the number of elements can be achieved and also the connection to the IF amplifier AMP_(IF) becomes easy.

Accordingly, according to the circuit of the present embodiment, a reduction of cost and reduction of size can be achieved.

As explained above, according to the present invention, an oscillator and a mixer which can achieve the reduction of the number of elements and can achieve a simplification of the circuit, reduction of cost, and reduction of size can be realized.

An explanation will be made next of a seventh embodiment of the present invention.

FIG. 11 is a circuit diagram showing the seventh embodiment of an integrated oscillation circuit portion of a television tuner according to the present invention.

Namely, IC denotes an integrated frequency conversion circuit; OSC_(U) denotes a UHF local oscillation circuit; SW denotes a switching circuit; LPF denotes a low pass filter; DT denotes a detection circuit; T₅₁ to T₅₄ denote input/output terminals used as the connection terminals with the external circuit etc.; RSN₈ denotes an external variable resonance circuit; R₉₇ an externally attached resistance element; C₅₂ and C₅₃ denote DC cutting capacitors; C₅₄ and C₅₅ denote capacitors for the positive feedback; and C₅₆ a connection capacitor, respectively.

Among these circuits, the UHF local oscillation circuit OSC_(U), the low pass filter LPF, the detection circuit DT, and the switching circuit SW are integrated, and the UHF local oscillation circuit OSC_(U) is connected via four input/output terminals T₅₁ to T₅₄ to the external variable resonance circuit RSN₈ and connected via the input/output terminal T₅₁ to the input end T₅₅ of the UHF/VHF mode changing signal S_(SW).

The local oscillation circuit OSC_(U) is constituted by a first Colpitz oscillation circuit, consisting of an npn-type oscillation transistor Q₁₀₁, and an npn-type oscillation transistor Q₁₀₂ for the load thereof, and a second Colpitz oscillation circuit consisting of an npn-type oscillation transistor Q₁₀₃, an npn-type transistor Q₁₀₄ for the load thereof, resistance elements R₉₁, R₉₃, and R₉₄, a biasing constant voltage source V₃₁ of the load transistors Q₁₀₂ and Q₁₀₄ and constant current sources I₅₁ and I₅₂.

The base of the oscillation transistor Q₁₀₁ is connected to the input/output T₅₁ and connected via the resistance element R₉₁ to the ground line GND, and the connection point between them is connected to the input of the low pass filter LPF.

The emitter of the oscillation transistor Q₁₀₁ is connected to the input/output T₅₂ and connected to the constant current source I₅₁, and the constant current source I₅₁ is connected to the ground line GND.

The collector of the oscillation transistor Q₁₀₁ is connected to the emitter of the transistor Q₁₀₂ for the load, and the output terminal O_(UT41) of the first Colpitz oscillation circuit is constituted by the connection point between them. This output terminal O_(UT41) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₁₀₂ is connected to the constant voltage source V₃₁, and the collector is connected to the line of the power source voltage V_(CC).

The base of the oscillation transistor Q₁₀₃ is connected to the input/output terminal T₅₄ and connected to the connection point between the resistance elements R₉₃ and R₉₄. The emitter of the oscillation transistor Q₁₀₃ is connected to the input/output terminal T₅₃ and connected to the constant current source I₅₂, and the constant current source I₅₂ is connected to the ground line GND. The collector of the oscillation transistor Q₁₀₃ is connected to the emitter of the load transistor Q₁₀₄, and the output terminal O_(UT42) of the second Colpitz oscillation circuit is constituted by the connection point between them. This output terminal O_(UT42) is connected to the not illustrated integrated mixing circuit MIX_(U).

The base of the load transistor Q₁₀₄ is connected to the constant voltage source V₃₁, and the collector is connected to the line of the power source voltage V_(CC).

The external variable resonance circuit RSN₈ is constituted by connecting the capacitor C₅₁ in parallel to the serial circuit of the variable capacitance diode CV₈ and the coil L₁₅.

The connection point between the coil L₁₅ of the external variable resonance circuit RSN₈ and the capacitor C₅₁ is connected via the DC cutting capacitor C₅₂ to the input/output terminal T₅₁ (base of the oscillation transistor Q₁₀₁), and the connection point between the anode of the variable capacitance diode CV₈ and the capacitor C₅₁ is connected via the DC cutting capacitor C₅₃ to the input/output terminal T₅₄ (the base of the oscillation transistor Q₁₀₃).

Also, the positive feedback capacitor C₅₄ is connected between the connection point between the capacitor C₅₂ and input/output terminal T₅₁ and the input/output terminal T₅₂, and the positive feedback capacitor C₅₅ is connected between the connection point between the capacitor C₅₃ and input/output terminal T₅₄ and the input/output terminal T₅₃.

Further, a coupling capacitor C₅₆ is connected between the connection point between the capacitor C₅₄ and the input/output terminal T₅₂ and the connection point between the capacitor C₅₅ and the input/output terminal T₅₃ (between the emitter of the oscillation transistor Q₁₀₁ and the emitter of the oscillation transistor Q₁₀₃).

The local oscillation circuit OSC_(U) is subjected to a positive feedback by the externally attached capacitors C₅₄ and C₅₅ connected between the base and emitter of the oscillation transistors Q₁₀₁ and Q₁₀₃ via the input/output terminals T₅₁, T₅₂, T₅₃, and T₅₄. It oscillates by the resonance frequency of the external variable resonance circuit RSN₈ connected to respective bases of the oscillation transistors Q₁₀₁ and Q₁₀₃ and outputs the local oscillation frequency signal S_(LU) at the predetermined frequency from the output terminals O_(UT41) and O_(UT42) to the UHF mixing circuit MIX_(U).

Note that, the oscillation transistors Q₁₀₁ and Q₁₀₃ constituting the first and second Colpitz oscillation circuits perform oscillation operations of reverse phases to each other since the respective bases are mutually connected via the external variable resonance circuit RSN₈.

Accordingly, local oscillation frequency signals S_(LU) having reverse phases to each other are output from the output terminals O_(UT41) and O_(UT42).

Also, the externally attached resistance element R₉₇ is connected between the middle point B of connection between the input/output terminal T₅₁ and DC cutting capacitor C₅₂ and the input/output terminal TSW of the UHF/VHF mode changing signal S_(SW).

Accordingly, in the integrated frequency conversion circuit IC, the connection terminal between the base of the oscillation transistor Q₁₀₁ and the external variable resonance circuit RSN₈ and the input terminal of the UHF/VHF mode changing signal S_(SW) make common use of the one input/output terminal T₅₁.

Note that, the resistance value of the externally attached resistance element R₉₇ is set to the same value as that of the internal resistance element R₉₄.

In the local oscillation circuit OSC_(U), a voltage obtained by dividing the voltage of the UHF/VHF mode changing signal S_(SW), the level of which is changed by switching in accordance with the UHF/VHF mode, is applied as the biasing voltage to the base as the biasing terminal of the oscillation transistor Q₁₀₁ by the internal resistance element R₉₁ and the externally attached resistance element R₉₇.

Also, the internal resistance elements R₉₃ and R₉₄ are connected in series between the ground line GND and the line of the power source voltage V_(CC), and the voltage obtained by dividing the voltage of the power source voltage V_(CC) by the two resistance elements R₉₃ and R₉₄ is applied as the biasing voltage to the base as the biasing terminal of the oscillation transistor Q₁₀₃.

The low pass filter LPF is constituted by the resistance element R₉₆ and the capacitor C₆₀, attenuated the oscillation signal between the oscillation signal appearing at the connection point A via the input/output terminal T₅₁ and UHF/VHF mode changing signal S_(SW), to obtain only the DC component, and outputs the same to the detection circuit DT.

In this low pass filter LPF, one end of the resistance element R₉₆ constitutes the input end, which is connected to the oscillation transistor Q₁₀₁ and the connection point between the input/output terminal T₅₁ and the resistance element R₉₁, the other end of the resistance element R₉₆ is connected to one electrode of the capacitor C₆₀, the other electrode of the capacitor C₆₀ is connected to the ground line GND, and the connection point between the other end of the resistance element R₉₆ and one electrode of the capacitor C₆₀ constitutes the output end, which is connected to the input of the detection circuit DT.

The detection circuit DT is constituted by a differential operation type comparator comprising the pnp-type transistors Q₁₀₈ and Q₁₀₇, the constant voltage source V₃₂, and the constant current source I₅₃, detects the level of the UHF/VHF mode changing signal S_(SW) input with a level in accordance with the operation mode, and outputs the detection signal S_(DT) of a level in accordance with the detection level to the switching circuit SW.

In this detection circuit DT, the base of the pnp-type transistor Q₁₀₈ constitutes the input end, which is connected to the output end comprising the connection point between the other end of the resistance element R₉₆ of the low pass filter LPF and one electrode of the capacitor C₆₀. The emitter of the pnp-type transistor Q₁₀₈ is connected to the constant current source I₅₃, and the collector is connected to the ground line GND. Also, the constant current source I₅₃ is connected to the power source voltage V_(CC).

The base of the pnp-type transistor Q₁₀₇ is connected to the constant voltage source V₃₂, the emitter is connected to the constant current source I₅₃, and the collector constitutes the output end of the detection signal S_(DT), which is connected to the input of the switching circuit SW.

Note that, the constant voltage source V₃₂ determines the threshold level of the UHF/VHF operation. The level thereof is set up to the value at the intermediate level between the base potential of the oscillation transistor Q₁₀₁ determined by the division of resistor of the internal resistance element R₉₁ and the externally attached resistance element R₉₇ and "0 V".

The switching circuit SW is constituted by the switching operation npn-type transistors Q₁₀₅ and Q₁₀₆, the resistance element R₉₅, and the constant current source I₅₄ and complementarily turns ON and OFF the UHF system current source and VHF system current source, which are not illustrated, in accordance with the input level of the detection signal S_(DT).

In this switching circuit SW, the base of the switching transistor Q₁₀₅ is connected via the resistance element R₉₅ to the collector of the switching transistor Q₁₀₆, the emitter is connected to the ground line GND, and the collector is connected to the not illustrated UHF system current source.

The base of the switching transistor Q₁₀₆ constitutes the input end, which is connected to the collector of the pnp-type transistor Q₁₀₇, which is the output end of the detection circuit DT. The emitter of the switching transistor Q₁₀₆ is connected to the ground line GND, the connection point between the collector and the resistance element R₉₅ is connected to the constant current source I₅₄, and the constant current source I₅₄ is connected to the line of the power source voltage V_(CC). Also, the connection point between the collector and the resistance element R₉₅ and the connection point with the constant current source I₅₄ is connected to the not illustrated VHF system current source.

An explanation will be made next of the operation by the above-described configuration. Note that, here, an explanation will be made of the mode changing operation between UHF and VHF, and an explanation for the oscillation operation of the local oscillation circuit OSC_(U) will be omitted.

At the VHF operation, the UHF/VHF mode changing signal S_(SW) of the low level "0 V" is input by for example a not illustrated external control system to the input end T₅₅. Alternatively, the input end T₅₅ is made open.

The UHF/VHF mode changing signal S_(SW) input to the input end T₅₅ is input from the input/output terminal T₅₁ to the integrated circuit IC via the externally attached resistance element R₉₇, input to the base of the oscillation transistor Q₁₀₁ through the connection point A, and input to the low pass filter LPF. At this time, the base of the transistor Q₁₀₁ becomes "0 V".

At the low pass filter LPF, the DC component is obtained, and that DC component is input to the base of the pnp-type transistor Q₁₀₈ of the detection circuit DT. At this time, the UHF/VHF mode changing signal S_(SW) is "0 V", and therefore also the input DC component is "0 V".

Accordingly, the base potential of the pnp-type transistor Q₁₀₈ becomes lower than the base potential of the pnp-type transistor Q₁₀₇, the pnp-type transistor Q₁₀₈ is retained in the ON state, and the pnp-type transistor Q₁₀₇ is retained in the OFF state.

AS a result, the current of the constant current source I₅₃ is all passed to the pnp-type transistor Q₁₀₈, and therefore the collector of the pnp-type transistor Q₁₀₇ becomes "0 V". By this, the detection signal S_(DT) of "0 V" (low level) is input to the base of the switching transistor Q₁₀₆ of the switching circuit SW.

Along with this, the base potential of the switching transistor Q₁₀₆ becomes "0 V", and therefore the switching transistor Q₁₀₆ is retained in the OFF state.

Accordingly, the current by the constant current source I₅₄ is supplied to the VHF current source. Along with this, the driving current is supplied to the VHF mixing circuit MIX_(V) and local oscillation circuit OSC_(V).

Also, the current by the constant current source I₅₄ is applied to the base of the switching transistor Q₁₀₅ as the predetermined signal voltage via the resistance element R₉₅.

By this, the switching transistor Q₁₀₅ is retained in the ON state, and as a result, the UHF system current source connected to the collector becomes OFF.

Accordingly, the driving current is not supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

Contrary to this, at the UHF operation, the UHF/VHF mode changing signal S_(SW) of the high level "9 V", the same level as that of the power source voltage V_(CC), is input to the input end by for example a not illustrated external control system.

The UHF/VHF mode changing signal S_(SW) input to the input end T₅₅ is input from the input/output terminal T₅₁ to the integrated circuit IC via the externally attached resistance element R₉₇, input to the base of the oscillation transistor Q₁₀₁ via the connection point A and, at the same time, input to the low pass filter LPF. At this time, the base of the oscillation transistor Q₁₀₁ becomes the potential obtained by dividing "9 V" by the internal resistance element R₉₁ and the externally attached resistance element R₉₇. The potential at the point A at this time is defined as "V_(A) ".

Also, the oscillation signal fed back as a positive feedback by the externally attached capacitor C₅₄ appears at the connection point A via the input/output terminal T₅₁ and is input to the low pass filter LPF.

At the low pass filter LPF, the oscillation signal is attenuated, so that the DC component is obtained, and that DC component is input to the base of the pnp-type transistor Q₁₀₈, of the detection circuit DT. V₃₂ is determined at the potential at an intermediate level between "V_(A) " and "0 V", whereby the base potential of the of the pnp-type transistor Q₁₀₇ is raised over the base potential of the pnp-type transistor Q₁₀₇, the pnp-type transistor Q₁₀₇ is retained in the OFF state, and the pnp-type transistor Q₁₀₇ is retained in the ON state.

As a result, the current of the constant current source I₅₃ is all passed through the pnp-type transistor Q₁₀₇, and therefore the collector of the pnp-type transistor Q₁₀₇ becomes the high potential (high level). By this, the high level detection signal S_(dt) is input to the base of the switching transistor Q₁₀₆ of the switching circuit SW.

By this, the base potential of the switching transistor Q₁₀₆ becomes the high level, and therefore the switching transistor Q₁₀₆ is retained in the ON state.

Accordingly, the current by the constant current source I₅₄ flows through the switching transistor Q₁₀₆, not supplied to the VHF current source, and the collector side of the switching transistor Q₁₀₆ is retained at "0 V". Along with this, the driving current is not supplied to the VHF mixing circuit MIX_(V) and local oscillation circuit OSC_(V).

Also, since the collector side is retained at "0 V" at the switching transistor Q₁₀₆, the base potential of the switching transistor Q₁₀₅ becomes "0 V", and therefore the switching transistor Q₁₀₅ is retained in the OFF state.

By this, the UHF system current source connected to the collector of the switching transistor Q₁₀₅ is turned ON. Accordingly, the driving current is supplied to the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U).

As explained above, according to the present embodiment, the configuration is made so that, in the integrated frequency conversion circuit IC constituted by forming the UHF mixing circuit MIX_(U) and local oscillation circuit OSC_(U), VHF mixing circuit MIX_(V) and local oscillation circuit OSC_(V), and the IF amplifier which amplifies the intermediate frequency signal by the UHF mixing circuit MIX_(U) and the intermediate frequency signal by the VHF mixing circuit MIX_(V) into a single chip, for the terminal for changing between the UHF and VHF modes, common use is made of the input/output terminal T₅₁ for the connection with the external variable resonance circuit RSN, of the UHF local oscillation circuit OSC_(U), the level of the UHF/VHF mode changing signal S_(SW) input at the level in accordance with the mode is detected at the detection circuit DT, the detection signal S_(DT) of the level in accordance with the detection level is input to the switching circuit SW, and the UHF system current source and the VHF system current source are complementarily turned ON and OFF, and therefore a reduction of the number of terminals can be achieved.

As a result, there are the advantages in that it becomes possible to accommodate the integrated frequency conversion circuit IC in a small package, the reduction of the parasitic oscillation and lowering of gain can be achieved, and a reduction of size of the tuner etc. and a reduction of the cost can be achieved.

Note that, in the circuit of FIG. 11, the resistance element _(R) ₉₄ and the resistance element R₉₇ for the voltage division are an internal resistor and external resistor, and accordingly there occurs a difference between the resistance values, and a slight potential difference is sometimes produced at the base bias between the oscillation transistors Q₁₀₁ and Q₁₀₃.

However, the current and the collector potential are set under the same conditions inside the IC, and also the DC component of the external variable resonance circuit RSN₈ is cut by the capacitance connection, and therefore this has no influence upon the differential oscillation characteristic of the local oscillation circuit OSC_(U).

As explained above, according to the present invention, a reduction of the number of terminals can be achieved, and as a result, it becomes possible to accommodate the integrated circuit in the small package, a reduction of the parasitic oscillation and lowering of gain can be achieved, and a reduction of size of the applied tuner and a reduction of cost can be achieved. 

What is claimed is:
 1. An integrated oscillation circuit comprising:a connection terminal connected to an external resonance circuit and an input line of a mode switching signal which is set at a different level in response to an operation mode; an oscillation element, a bias terminal of which is connected to said connection terminal; a detection circuit detecting the level of said mode switching signal applied to said bias terminal of said oscillation element; and a switching circuit turning on or off a power source for driving said oscillation element in response to said level detected at said detection circuit.
 2. An integrated oscillation circuit according to claim 1, further comprising a filter provided between said bias terminal and said detection circuit, said filter attenuating said mode switching signal to provide a DC component.
 3. An integrated oscillation circuit according to claim 1, wherein said oscillation element comprises an npn-type transistor, andwherein said detection circuit comprises a differential operation type comparator including a pair of pnp-type transistors having emitters which are connected to current sources, a base of one of said pnp-type transistors being applied with said mode switching signal, and a base of other of said pnp-type transistors being applied with a signal having a predetermined set level.
 4. An integrated oscillation circuit comprising:a connection terminal connected to an external resonance circuit and an input line of a mode switching signal which is set at a different level in response to an operation mode; an oscillation element, a bias terminal of which is connected to said connection terminal; a detection circuit detecting the level of said mode switching signal applied to said bias terminal of said oscillation element; a switching circuit turning on or off a power source for driving said oscillation element in response to said level detected at said detection circuit; and a filter provided between said bias terminal and said detection circuit, said filter attenuating said mode switching signal to provide a DC component.
 5. An integrated oscillation circuit according to claim 4, wherein said oscillation element comprises an npn-type transistor, andwherein said detection circuit comprises a differential operation type comparator including a pair of pnp-type transistors having emitters which are connected to current sources, a base of one of said pnp-type transistors being applied with said mode switching signal, and a base of other of said pnp-type transistors being applied with a signal having a predetermined set level.
 6. An oscillator comprising:a first oscillating circuit including a first oscillation transistor pair connected to a first resonance circuit, and a buffer transistor pair connected to said first oscillation transistor pair and having a first load element for outputting a first oscillation signal having a first frequency; and a second oscillating circuit including a second oscillation transistor pair connected to a second resonance circuit and said first load element and outputting a second oscillation signal having a second frequency.
 7. An oscillator according to claim 6, wherein said first oscillating circuit and said second oscillating circuit are complementary turned on and off. 